Recent Advances in the Study of Heredity. 163 
sense view of the matter, is held all the more firmly and deeply 
because it is held to a large extent unconsciously. It “ stands to 
reason ” that if you go on breeding long enough from Andalusian 
fowls you will ultimately obtain a pure race of them. 
It is important to recognize, so far as we can, the exact nature 
of the general theory of inheritance which directed speculation and 
practical breeding during the period preceding the revolution 
initiated by Weismann ; and this I have attempted to do by tracing 
it to that conception of inheritance (entertained dimly by Lamarck 
and definitely by Charles Darwin) which calls for some explanation 
of the mechanism by which the characters of an organism are 
impressed on the germ-cells which it contains. 
The Third Period. 
The revolution in opinion which may be said to consist in the 
perception that the answer to the question “ which came first, the 
hen or the egg ?,” is “the egg,” was, as I have said, initiated by the 
publication of Weismann’s theory of the continuity of the germ- 
plasm in 1885. The revolution has consisted in a swinging round 
of our point of view through 180 degrees. We no longer look from 
the soma to the germ, but from the germ to the soma. We no 
longer ask ourselves : how do the characters of an organism get 
into the germ-cells which it produces ? but, how are the characters 
of an organism represented in the germ-cells which produce it ? 
But though the majority of biologists do lip-service to Weismann’s 
view of the matter, many of them retain, or have done until very 
recently, a belief in the theory of ancestral contributions, which is 
diametrically opposed to the Weismannian conception. Men’s 
relation to new theories seems to me to have been always the same. 
They do not first take hi a new theory and then announce their 
adhesion to it; they first announce their adhesion to it and then 
gradually take it in. Indeed it is only now that people are beginning 
to believe that the characters of organisms are determined by the 
potentialities in the germ-cells which give rise to them, and not by 
the somatic characters of their parents or their ancestors. 
That which has been most effective in converting biological 
opinion to this theory has been the body of fact and hypothesis 
which we owe to Mendel and those who have worked on the lines 
laid down by him. And it seems worth while to consider briefly the 
relation between Weismann and Mendel. It has been argued by 
